Method for treating metals



United btates Patent METHOD FOR TREATING METALS Marshall B. Aipert, New Dorp, N. Y., assignor to Iflational Lead Company, New York, N. Y., a corporation of New .lersey No Drawing. Application June 1, 1953, Serial No. 358,973

5 Claims. (or. 117 130 This invention relates to a method for treating metals. More specifically it relates to a method for coating base metals. Further it relates to a method for coating fl'le surface of a base metal with titanium metal.

Titanium metal possesses the physical and chemical characteristics of being particularly resistant toward corrosion and of being resistant to wear. Since titanium metal has these remarkable qualities it is desirable therefore to coat base metals with a continuous titanium metal coating so that the coated base metal can be used for some of the same purposes for which titanium metal itself is used. Titanium metal is fairly expensive whereas cheap base metals coated with titanium metal would be relatively inexpensive. Such coated base metals are therefore highly desirable since they could be used in place of the highly resistant titanium metal.

An object of this invention, therefore, is to provide a method for coating a base metal with a continuous coating of titanium metal. A still further object of this invention is to provide a process for coating a base metal which is simple and easy to operate. A still further object is to provide a coated base metal which has some of the physical properties which are similar to titanium metal itself. These and other objects will become apparent from the following more complete descriptionof the instant invention. a v I Broadly this invention contemplates a method for coating a base metal with titanium metal which comprises placing the base metal in a bath containing reduced titanium halide selected from the group consisting of titanium dihalide and titanium trihalide and a fused salt selected from the group consisting of alkali metal halide and alkaline earth metal halide at a temperature of at least about 800 C., maintaining a high molality of re duced halides in said bath and maintaining a high ratio of titanium dihalide to titanium trihalide during said process until said base metal is coated with titanium metal.

The temperature of the operation should die between about 800 C. to a temperature where the salt becomes excessively volatile or where the base metal is either melted or the physical properties of the base metal are adversely affected. For ease of operation and equipment design it is preferable to operate at temperature from about 800 C. to about 1100 C.

Substantially any base metal which lies below titanium in the Electrochemical Series may be employed. Most of these metals have a melting point about 1100 C. and therefore may be easily coated without adversely affecting the physical properties of the base metal employed. In the case of the base metals which have relatively low melting points it must be remembered that the temperature of the operation should be below the temperature at which the base metal will be seriously altered.

As pointed out above, the method of the instant invention employs a fused salt bath in which the operation is conducted. This bath may consist of any alkali metal halide and alkaline earth metal halide or combinations of such compounds. Mixtures of these compounds which form low melting point eutectics are particularly advantageous since lower temperatures of operation may be employed. These low temperatures are particularly desirable in order to prevent the physical properties of the base metal from being adversely affected. Although any halide may be employed, it is particularly desirable to use chlorides since they are more economical and more readily available for employment.

An atmosphere of argon or other inert gas is preferably maintained above the fused salt bath in order to prevent contamination of the titanium values by the outside atmosphere.

As stated above, the method is simple to conduct since it comprises merely placing the base metal to be coated into a fused salt bath at a temperature above about 800 C. and having present in the bath a quantity of reduced titanium halide preferably titanium dichloride. The concentration of the reduced titanium halide may be Varied considerably. The concentration of the reduced titanium halides in the bath should be at least 0.1 molal; however, for most efiicient results it is desirable to have a much higher concentration of reduced titanium halide values in the bath. In fact it is desirable to approach the maximum solubility of the reduced titanium halide in the bath as the process is being carried out.

The titanium values present in the fused salt bath as reduced titanium halides may be formed chemically or electrochemically in the container itself or may be prepared externally and added to the container. A convenient way of preparing reduced titanium chloride containing ahigh quantity of titanium dichloride is to pass titanium tetrachloride through a bed of titanium metal.

The titanium values as stated above must be present in soluble form in the bath as reduced titanium halides. In the case of chloride it is desirable to maintain the reduced titanium chlorides mostly in the divalent form as titanium dichloride. In fact it is desirable to maintain a minimum amount of titanium trichloride in solution by maintaining the titanium dichloride to titanium trichloride ratio close to the equilibrium value set by the reaction Ti+2TiClafi3TiCla In most cases it has been found that the equilibrium state is obtained when substantially to of the titanium values are present as titanium dichloride. Many methods may be utilized for maintaining this high ratio of titanium dichloride to titanium trichlon'de. One method of maintaining this condition is to have present during the operation titanium metal particles in the bath. Scrap titanium metal may be used for this purpose.

As previously stated, the base metal placed in the fused salt bath containing a high concentration of titanium values in a reduced titanium halide state is thereby coated by titanium metal. It is believed that the titanium values in the bath disproportionate to form a titanium metal alloy with the surface of the base metal. At the same time as more titanium is deposited on the coating, the titanium in the alloy gradually difiuses further into the base metal then producing a coating which is substantially free from base metal at the surface With decreasing amounts of titanium in the alloy below the surface. This coating is formed substantially without any solubilization of the base metal. The coatings vary in thickness depending upon the conditions of operation which particularly include the type of base metal employed, the temperature and time of operation and the amount of reduced titanium halides present in the salt bath. Coatings from 0.001 and 0.02 inch in thickness have been obtained. These coatings are continuous and the base metals which have been coated with titanium metal may be. usedinplaceof titanium metal for many purposes.

In order to further illustrate the instant invention, the following examples are presented.

Example 1 A fused salt consisting of 100 parts of sodium chloride was placed in a tightly sealed silica container. To this salt mixture were added 60 parts of reduced titanium chloride which contained 87% of the titanium in the divalent form and 13% of the titanium in the trivalent form. In order to maintain a high percentage of titanium dichloride in the mixture 10 parts of scrap titanium metal were also added, The mixture was then heated to 900 C. and a base metal iron rod was inserted into the bath. The rod was coated with a continuous titanium metal coating 0.0128 inch thick after 45 hours. This titanized rod was acid resistant to substantially the same extent as a rod of titanium metal.

Example 2 Example 1 was repeated except that 73 parts of strontium chloride and 27 parts of sodium chloride were used instead of the sodium chloride alone to prepare the fused salt bath and substantially the same results were obtained.

Example 3 Example 1 was repeated except in this example a tantalum metal strip was used as the base metal and after 66 hours at 930 C. a continuous coating 0.0014 inch thick was obtained.

Example 4 Example 1 was repeated except that a nickel metal rod was used. The continuous coating was 0.0048 inch thick after treatment at 840 C. for 66 hours.

Example 5 Example 1 was repeated except that a graphite rod was used as the base metal. A titanium carbide coating penetrating to a depth of about 0.005 inch thick on the graphite rod was obtained after 164 hours at 950 C.

From the above description and by the examples shown, it is seen that a base metal has been coated with a continuous film of titanium metal by the process of the instant invention. The method is easy and simple to operate. The base metal which is coated with a continuous coating of titanium metal may be used for many of the same purposes which titanium metal itself is employed, and the coated base metal is relatively inexpensive in comparison to the cost of employing titanium metal itself for these purpose. Such coated base metals possess many properties similar to titanium metal and therefore can be used in place of the titanium metal itself.

While this invention has been described and illustrated by the examples shown, it is not intended to be limited thereto and other modifications and variations may be employed within the scope of the following claims.

I claim:

1. A method for coating the surface of a base metal which lies below titanium in the Electrochemical Series which comprises placing the base metal in a bath containing reduced titanium halide selected from the group consisting of titanium dihalide and titanium trihalide and a fused salt selected from the group consisting of alkali metal halide and alkaline earth metal halide at a temperature of at least about 800 C. to below the temperature at which the physical properties of the base metal, are adversely, afiected and the. fused salt volatilizes; maintain ing a high molality of reduced halides in said bath and maintaining a high ratio of titanium dihalide to titanium trihalide during said process until said base metal is coated with titanium, metal.

2. Process according to claim 1 in which the. reduced titanium halide is chloride and in which the ratio of titanium dichloride to titanium trichloride is held close to the equilibrium value set by the reaction 3. Process according to claim 1 in which the reduced titanium halide molality in the bath is at least 0.1 molal.

4. Process according to claim 1 in which the ratio of titanium dihalide to titanium trihalide is maintained by the presence of titanium metal in the bath.

5. Process according to claim 1 in which the titanium metal coating on the base metal is from 0.001 to 0.02 inch thick.

References Cited in the file of this patent UNITED STATES PATENTS 1,405,167 Shoemaker Jan. 31, 1922 1,497,417 Weber June 10, 1924 2,551,341 Scheer et a1. May 1, 1951 

1. A METHOD FOR COATING THE SURFACE OF A BASE METAL WHICH LIES BELOW TITANIUM IN THE ELECTROCHEMICAL SERIES WHICH COMPRISES PLACING THE BASE METAL IN A BATH CONTAINING REDUCED TITANIUM HALIDE SELECTED FROM THE GROUP CONSISTING OF TITANIUM DIHALIDE AND TITANIUM TRIHALIDE AND A FUSED SALT SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL HALIDE AND ALKALINE EARTH METAL HALIDE AT A TEMPERATURE OF AT LEAST ABOUT 800* C. TO BELOW THE TEMPERATURE AT WHICH THE PHYSICAL PROPERTIES OF THE BASE METAL ARE ADVERSELY AFFECTED AND THE FUSED SALT VOLATILIZES, MAINTAINING A HIGH MOLALITY OF REDUCED HALIDES IN SAID BATH AND MAINTAINING A HIGH RATIO OF TITANIUM DIHALIDE TO TITANIUM TRIHALIDE DURING SAID PROCESS UNTIL SAID BASE METAL IS COATED WITH TITANIUM METAL. 